Method for cutting sheet material with variable gain closed loop

Abstract

A method for cutting limp sheet material with a rigid, cantilevered blade that is reciprocated as it advances along a cutting path through sheet material employs a load sensor to measure lateral loads applied to the blade by the sheet material during cutting. A load signal from the sensor is applied to the blade controls through a variable gain feedback circuit and causes the blade to be oriented slightly toward the side of the cutting path from which an unbalanced load is applied. The adjustment of the gain in the feedback network is made by means of speed sensors which measure the rate at which the cutting blade advances through the sheet material and adjust the feedback gain in inverse relationship.

We claim: 
     
       1. A method of cutting limp sheet material with a cutting blade comprising: advancing the cutting blade and sheet material relative to one another in cutting engagement and generally tangent to a desired cutting path;   sensing lateral loads applied to the blade by the sheet material as the blade is advanced;   orienting the blade slightly out of a position tangent to the cutting path as the blade is advanced to oppose the lateral loads applied to the blade; and   regulating the amount by which the blade is oriented out of the tangent position in accordance with the sensed lateral load on the blade and an adjustable gain factor influencing the effect of lateral load on blade orientation; and   adjusting the gain factor as the blade advances in accordance with the rate at which the blade and material are advanced relative to one another.   
     
     
       2. A method of cutting limp sheet material as defined in claim 1 wherein the step of adjusting includes decreasing the gain factor to reduce the amount by which the blade is oriented out of the tangent position at a given lateral load as the rate of advancement increases. 
     
     
       3. A method of cutting limp sheet material as defined in claim 1 wherein the cutting blade is a cantilever-mounted knife blade. 
     
     
       4. A method of cutting limp sheet material as defined in claim 1 wherein the step of regulating comprises regulating the amount by which the blade is oriented in direct relationship with the sensed lateral load and the step of adjusting comprises adjusting the gain factor in inverse relationship with the rate of advancement. 
     
     
       5. A method of cutting limp sheet material as defined in claim 1 wherein the step of advancing comprises advancing a rigid cantilever-mounted knife blade along a cutting path relative to the sheet material in cutting relationship; and the step of orienting comprises orienting the advancing knife blade toward the side of the cutting path from which a lateral load bending the cantilevered knife blade is applied. 
     
     
       6. A method of cutting limp sheet material as defined in claim 5 wherein: the step of advancing comprises advancing the rigid, cantilever-mounted knife blade along a cutting path through a multi-ply layup of limp sheet material with depending portion of the blade in the layup whereby forces from the layup are developed on the depending portion of the blade.   
     
     
       7. A method of cutting limp sheet material as defined in claim 6 further including the step of evacuating air from the layup of sheet material in the region being cut during the steps of advancing and sensing. 
     
     
       8. A method of cutting limp sheet material with a cutting blade in an automatically controlled cutting machine comprising: advancing the cutting blade and sheet material relative to one another in cutting engagement and generally tangent to a desired cutting path in the material;   sensing lateral loads applied to the blade by the sheet material as the blade is advanced and producing load signals representative of the sensed lateral loads on the cutting blade;   amplifying the sensed lateral load signals with an adjustable gain factor;   adjusting the gain factor upwardly and downwardly in inverse relationship with the rate of advancement of the cutting blade and sheet material; and   orienting the cutting blade out of the tangent position by an amount determined by the amplified load signal.